1. Field of the Invention
The present invention relates to a portable terminal for use in a mobile communication system based on the CDMA (Code Division Multiple Access) technique, and more particularly to a portable terminal that is capable of reducing power consumption in the generation of profile data.
2. Description of the Related Art
When a portable terminal for use in a CDMA mobile communication system receives a signal transmitted via a radio link, it despreads the received signal and outputs audio or video data based on the despread signal. Though it is necessary to recognize the timing of transmission of the signal from the base station, the portable terminal is unable to recognize the timing of transmission of the signal from the base station.
In order to detect a point (timing) to start despreading the received signal, it has been customary for the portable terminal to calculate correlated values between a plurality of known patterns that have been internally generated and the received data, generate profile data based on the calculated correlated values, and detect the timing to start despreading the received signal from a peak value of the profile data.
The portable terminal for use in the CDMA mobile communication system has heretofore been required to reduce power consumption because it performs a transmission power control process and other complex control processes.
The accuracy with which to detect a received pilot signal required to generate profile data in the above conventional portable terminal may be increased by increasing the number of sampling points. However, increasing the number of sampling points results in an increase in the power consumption by the portable terminal.
It is therefore an object of the present invention to provide a portable terminal which is capable of reducing power consumption without lowering the accuracy with which to generate profile data.
According to the present invention, a portable terminal has a level detector which compares profile data generated by a profile generator with a threshold value, and determines a sampling rate for a correlating process performed by a correlator based on the result of the comparison. The sampling rate is determined in order to increase the sampling rate at profile points in excess of the threshold value, of the profile data. Therefore, profile data is generated highly accurately at a higher sampling clock rate at points which require a higher accuracy, and profile data is generated at a lower sampling clock rate at points which do not require such a higher accuracy.
Only at the points which require a higher accuracy, the number of sampling points is increased and profile data is generated at the higher sampling clock rate. At the point which do not require a higher accuracy, the number of sampling points is reduced and profile data is generated at the lower sampling clock rate. Consequently, highly accurate profile data can be generated while at the same time the power consumption is reduced and the circuit scale of the portable terminal is reduced.